Percussion circuit for electronic organs



May 14, 1968 P. H. SHARP PERCUSSION CIRCUIT FOR ELECTRONIC ORGANS FiledJune 2s, 1965 14 l 5k-: 21 T101 7c3 /L/ Fira. 3.

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United States Patent O 3,383,453 PERCUSSION CIRCUIT FOR ELECTRONICORGANS Paul H. Sharp, Electro Music, P.O. Box 2267D, Altadena, Calif.91105 Continuation-impart of application Ser. No. 214,331, Aug. 2, 1962.This application June 28, 1965, Ser. No. 467,219

Claims. (Cl. 841.26)

This application is a continuation-in-part of my prior application Ser.No. 214,331, filed Aug. 2, 1962, entitled Percussion Circuit Utilizing aSingle-Pole Key Switch, now Patent No. 3,244,790, issued Apr. 5, 1966.

Percussive effects can be crudely produced on a conventional electronicorgan by depressing a key and immediately releasing it. Immediaterelease is required because, in the conventional organ circuit, the tonecontinues as long as the key is depressed. In contrast, a piano key canbe held down or released without altering the tone. Thus percussivetones are produced by imparting a burst of energy to a vibrating body,rather than a continuous supply of energy. After the energy pulse isinitially applied to a percussive tone generator, it decays at a ratedetermined by the damping characteristics of the generator.

Some electronic organs utilize circuits that require, for the productionof percussive effects, continued depression of a key. This, too, is anunnatural operation as compared, for example, to the piano. Otherelectronic organs superimpose a percussion envelope on the entire organoutput. This severely restricts versatility.

One of the primary objects of this invention is to provide improvedcircuitry for producing percussive eiTects in which the organ key, afterdepression, can be released or not without affecting the tone produced.Thus the action truly simulates that of a piano or equivalent percussiveinstrument.

In still other known organ circuits for producing percussive effects, akey-operated switch has both a backcontacting and a front-contactingposition. In such organizations, movement of the switch rst disconnectsa capacitor from a source, and then connects it to a tone generator.These circuits have proved impractical since' they require majorrevisions in the conventional singlepole switch assemblies used inelectronic organs. Further, they require undue maintenance to ensureproper engagement of a switch arm with a back contact and a frontcontact. Such adjustments are ordinarily not required.

Accordingly, an important object of this invention is to provide meansfor producing percussive effects by the natural key manipulationdescribed with the aid of a simple single-pole switch. This means thatexisting switch assemblies can be utilized.

Another object of this invention is to lprovide simple circuits by theaid of which two transient periods for operation of a tone generator maybe determined, corresponding to initial closure of a single-pole keyswitch, and Iopening thereof.

This invention possesses many other advantages, and has other objectswhich may be made more clearly apparent from a consideration of severalembodiments of the invention. For this purpose, there are shown a fewforms in the drawings accompanying and forming part of the presentspecication. These forms will now be described in detail, illustratingthe general principles of the invention; but it is to be understood thatthis detailed description is not to be taken in a limiting sense, sincethe scope of the invention is best defined by the appended claims.

Referring to the drawings:

FIGURE 1 is a diagram of one form of the present invention;

ICS

FIG. 2 is a circuit diagram equivalent to that of FIG. 1; and

FIG. 3 is a circuit diagram of a modified form of the present inventionin which one of the transient circuits incorporates a normally chargedrather than a normally discharged condenser.

In FIG. 1, a typical piano gate circuit incorporating the presentinvention is illustrated. Within the rectangle is a typical transistoramplifier that operates upon a signal of constant amplitude provided bya tone generator (not shown) for a particular note. This signal,corresponding, say, to Fil, is applied to an input terminal T1. Througha transistor Q1, this signal is translated to an output terminal T2. Theamplitude of the signal at the output depends upon the conductivity ofthe transistor Q1. This, in turn, is determined by two factors, thecut-off bias imposed upon the base of the transistor, and a superimposedsignal.

Cut-otl bias is provided by a suitable adjustable voltage source througha resistor R6 that connects with the transistor base. The superimposedsignal is provided by a transient circuit formed by elements outside therectangle. The superimposed signal appears at the terminal`T3 and isapplied through a resistor R3 to the transistor base. In the presentexample, the voltage at the terminal T3 is normally about zero. Uponclosure of a switch S, the voltage at the terminal T3 instantly rises,and then decays, and the amplitude of the output signal iscorrespondingly determined to simulate a percussive tone.

The shape of the decay characteristics is adjusted by the bias `adjustcircuit and by components R5, R4, D3. The remaining components determinethe basic decay characteristic. R3 has a value many times greater thanthe input resistance of the amplifier; hence, the mechanics for theproduction of the basic decay characteristic can be examined by the aidof an equivalent circuit (FIG. 2) in which the amplifier is replaced bya zero impedance. Thus R3 is now connected directly across the terminalT3 and the lead L1. In this equivalent circuit, the components thatmerely adjust the shape of the decay characteristics likewise areomitted.

In FIG. 2, R3, enclosed in a circle, thus represents a tone generatorthat produces a signal the intensity of which is directly proportionalto applied Voltage or current. It will be understood that R3 representsthe equivalent input impedance of an oscillator or keyer for acontinuously operating generator or the like. That impedance mayincorporate reactive elements.

A small battery B (which may be a suitable DJG. power supply common toall circuits) serves as a source of voltage for application to thegenerator R3. When the key switch S is closed, a series circuit isestablished through series connected capacitors C1 and C2. Thegenerat-or R3 parallels the operating capacitor C2; the other capacitorserves a controlling function. The series circuit Ican be `traced fromone side of the battery B, switch S, controlling capacitor C1, a reverseblocking diode D2, capacitor C2, and lead L1 to Ithe other side of thebattery B or source. As soon as the switch closes, the source voltagedivides between the two capacitors, and about 99% of the voltage appearsacross C2 because the capacity of C1 is about 100 times that of C2.Accordingly, immediately upon switch closure, a high signal level isproduced.

At this instant of switch closure, the controlling capacitor C1 has verylittle charge; but `a charging circuit is provided through R2 so long asthe switch S is kept closed. At the same time, .the generator R3 forms adischarging circuit for the operating capaci-tor C2. The controllingcapacitor C1, however, has another very slowcharging circuit through R3and D2. Whether this supplemental charging circuit is effective dependsupon whether 3 D2 is forward biased or reverse biased. This, in turn,depends upon the time constants of the circuit.

The voltage at the `terminal T3 on the cath-ode side of D2 tends .tofall from the initial seven volts substantially 'in accordance with thetime constant CZ*R3. The voltage at the anode terminal T4 -tends t-ofall from the initial .seven volts substantially in accordance with thetime constant (l1-R2.

In the present example, the time constant C2-R3 is a good `deal shorterthan for Cl-RZ. Accordingly, the diode D2 remains 'forward biased, andthe supplemental charging circuit for the controlling condenser iseffective. The charging current for C1 through R3 adds to thedischarging current of C2. Both currents, of course, decay. But sinceboth are operative, the rate of decay is less than if the supplementalcharging circuit were not effective.

If the switch S is held down, ultimately C1 charges fully, and C2discharges fully, and the signal intensity is zero. However, if theswitch S is opened while the signal produces an audible sound, then thedecay rate changes. C1 now discharges very rapidly through -resistor R1and diode D1. Consequently, the current previously liowing throughresistor R3 for charging capacit-or C1 has ceased. Signal intensity nowreduces at a faster rate. The signal intensity continues to reduceacc-Ording to the time constant C2-R3. Release of the lswitch S producesa damping function much as the release of a piano key does.

By changing the values of the circuit elements, the time constant of thecharging resistor R2 and the controlling capacitor C1 can be made lessthan that of the generator R3 and operating capacitor C2. Ilf so, thenthe decay rate becomes independent of the continued depression of thekey S. Thus immediately upon switch closure, the full voltage appearsacross the operating capacitor C2. At the next instant of time, thediode D1 becomes reverse biased, and no supplemental charging circuitfor the controlling capacitor C1 is elective. The decay of voltageacross the generator R3 depends solely upon the capacity of thecapacitor C2 and the value of the irnpedance of R3. Operation thensimulates instruments having no key released dampers.

The circuit can take a number of forms. For example, a normally closedkey switch can be substituted with slight changes in the circuitarrangement. The polarities can also be reversed. Furthermore, thecontrol capacitor can be normally charged rather than normallyuncharged. In FIG. 3, there is illustrated a percussion circuit in whichthe polarities are reversed and the control capacitor C1 normallycharged;

When the switch is open, the control capacitor C1 is in series with asmall ohmic value resistor R1', a battery B', and a reverse blockingdiode D1. The terminal T4', on one side of the capacitor C1', is clampedto the voltage of the negative terminal at lead L1'. The other side ofthe control capacitor is at the voltage of the positive terminal of thebattery. Hence, the capacitor is normally fully charged. As soon as theswitch S' is closed, the operating capacitor C2 is connected directlyacross the control capacitor C1'. The circuit can be traced through`switch S', lead L1', capacitor C2', diode D2', capacitor C1', back tothe switch. Thev diode D2' is of such polarity as to allow the charge tobe immediately redistributed between the capacitors. The voltages acrossthe capacitors must now be the same. But since the operating capacitorC2' has a much smaller capacity, there is very little voltage drop. Assoon as the switch is closed, the source B1 is isolated from all circuitelements except Rl'. l

As in the previous form, the signal amplitude starts at a high level.The decay rate may depend upon the switch S' in accordance with the timeconstants of the circuit.

The operating capacitor` C2' has a discharge circuit through thegenerator yR3'. The control capacitor has a discharge circuit through aresistor R2. The diode D1' is now reverse biased. The control capacitorC1' has a supplemental discharge circuit through the generator R5' andthe diode D2. This circuit may or may not be eiective, depending uponcircuit Values. Thus the diode D2' may or may not be reverse biased.

IIf the circuit values are such that the diode D2' is reverse biased,then the signal decay characteristic depends upon C2' alone, whether theswitch S' is held down or not. If, however, the circuit values are suchas to forward bias the diode D2', then the signal decay characteristicdepends 'both upon the current produced by the control capacitor and theoperating capacitor so long as the key switch S' is held closed. Thusthe discharge circuits for C1 are then interrupted, and the chargingcircuit therefor again becomes operative. At the same time, theoperating capacitor C2' continues to discharge, but the sign-al leveldrops abruptly as the key switch S is opened. This simulates the keyreleased d-amper action of a piano.

By virtue of the fact that the control capacitorkhas a much greatercapacity than the operating capacitor, it is unnecessary to providespecial anti-pump up circuitry to -avoid voltage building upon rapidopening and closing of the key switch.

The inventor claims:

1. In an electrical musical instrument: an electrically operatedgenerating device that produces a signal correspondingto a musical tonewith an intensity related directly to the intensity of electricalenergization: an operating capacitor; an operating circuit for saidgenerating device including said operating capacitor; a single pole keyswitch cooperable with a source of direct current; a control capacitor;circuit means providing charging and discharging circuits for saidcontrol capacitor, and operable respectively in accordance with theposition of said key switch; and unidirectionally conductive meansinterconnecting the operating circuit and said control capacitor uponoperation of said key switch; said circuit means having characteristicsdetermining the continued electiveness of said unidirectionallyconductive means following key switch operation.

2. In an electrical musical instrument: an electrically operatedgenerating device that produces a signal corresponding to a musical tonewith an intensity related directly to the intensity of electricalenergization: an operating capacitor paralleling said generating devicewhereby charge applied to the operating capacitor energizes saidgenerating device; a control capacitor; a normally open single poleswitch cooperable with a source of direct lcurrent for connecting thecapacitors in series across said source; a diode between the capacitors,and polarized to permit the charging of said capacitors by said source;a resistor forming a first charging circuit for said control capacitorindependent of said diode; said generating device also providing asupplemental charging circuit for said control capacitor dependent uponsaid diode; said tirst charging circuit being designed to reverse biassaid diode immediately after switch closure whereby the decaycharacteristic of said generating device is independent of key switchopening.

3. The combination as set forth in claim 2 together with means forquickly discharging said control capacitor upon opening of said keyswitch.

4. In an electrical musical instrument: an electrically operatedgenerating device that produces a signal corresponding to a musical tonewith an intensity related directly to the intensity of electricalenergization: an operating capacitor paralleling said generating devicewhereby charge applied to the operating capacitor energizes saidgenerating device; a control capacitor; a normally open single poleswitch cooperable with a source of direct current for connecting thecapacitors in series across said source; a diode between the capacitors,and polarized to permit the charging of said capacitors by said source;a resistor forming a rst charging circuit for said control capacitorindependent of said diode; said generating device also providing asupplemental charging circuit for said control capacitor dependent uponsaid diode; said first charging circuit being designed to forward biassaid diode immediately following key switch closure whereby saidsupplemental charging circuit remains effective while said key switch isclosed.

5. The combination as set forth in claim 4 together with means forquickly discharging said control capacitor upon opening of said keyswitch.

6. In an electrical musical instrument: an electrically operatedgenerating device that produces a signal corresponding to a musical tonewith an intensity related directly to the intensity of electricalenergization: an operating capacitor paralleling said generating devicewhereby charge applied to the operating capacitor energizes saidgenerating device; a normally charged control capacitor; a normally opensingle pole switch for connecting the control capacitor across theoperating capacitor; a diode between the capacitors, and polarized topermit the exchange of charge between said capacitors upon closure ofsaid switch; a resistor forming a first discharging circuit for saidcontrol capacitor independent of said diode; said generating device alsoproviding a supplemental discharging circuit for said control capacitordependent upon said diode; said first discharging circuit being designedto reverse bias said diode immediately after switch closure whereby thedecay characteristic of said generating device is independent of keyswitch opening.

7. The combination as set forth in claim 6 together with means forquickly charging said control capacitor upon opening of said key switch.

8. In an electrical musical instrument: an electrically operatedgenerating device that produces a signal corresponding to a musical tonewith an intensity related directly to the intensity of electricalenergization: an operating capacitor paralleling said generating devicewhereby charge applied to the operating capacitor energizes saidgenerating device; a normally charged control capacitor; a normally opensingle pole switch for connecting the control capacitor across theoperating capacitor; a diode between the capacitors, and polarized topermit the exchange of charge between said capacitors upon closure ofsaid switch; a resistor forming a first discharging circuit for saidcontrol capacitor independent of said diode; said generating device alsoproviding a supplemental discharging circuit for said control capacitordependent upon said diode; said first discharging circuit being designedto forward bias said diode immediately following key switch closurewhereby said supplemental discharging circuit remains effective whilesaid key switch is closed.

9. The combination as set forth in claim 8 together with means forquickly charging said control capacitor upon opening of said key switch.

10. In an electrical musical instrument: an electrically operatedgenerating device that produces a signal corresponding to a musical toneIwith an intensity related directly to the intensity of electricalenergization: an operating capacitor and a control capacitor; circuitmeans connecting the capacitors including unidirectionally conductivemeans and a key switch; means providing a source of direct currentvoltage and operatively connected to said operating capacitor inaccordance with the position of said key switch; and means forming atransient circuit for said control capacitor effective upon operation ofsaid key switch, and having a characteristic to determine theconductivity characteristic of said unidirectionally conductive meansand the continued interconnection between said capacitors following keyswitch operation.

11. The combination as set forth in claim 10. in which said transientcircuit determines continued connection between said capacitorsfollowing key switch operation whereby said key switch operates as a keyreleased damper.

12. The combination as set forth in claim 10 in which said transientcircuit isolates said capacitors following key switch operation wherebysaid key switch operates as a clapper without a damper.

13. In an electrical musical instrument: an electrically operatedgenerating device that produces a signal corresponding to a musical tonewith an intensity related directly to the intensity of electricalenergization; an operating capacitor having a discharge path includingsaid generating device; a control capacitor; a single pole normally openswitch for transferring charge from the control capacitor to theoperating capacitor; means forming a discharge path for one of thecapacitors whereby the decay of voltage for the capacitors differs; anda unidirectionally conductive device for isolating the discharge pathprovided by said generating device in response to a disparity ofcapacitor voltages whereby the decay of current through the generatingdevice is independent of subsequent switch opening.

14. In an electrical musical instrument: an electrically operatedgenerating device that produces a signal corresponding to a musical tonewith an intensity related directly to the intensity of electricalenergization; an operating capacitor paralleling said generating devicewhereby charge applied to the operating capacitor energizes saidgenerating device; a control capacitor; a normally open single poleswitch for connecting the control capacitor across the operatingcapacitor; a resistor forming a supplemental discharge path for thecontrol capacitor; and a diode for isolating said resistor from saidsupplemental discharge path and for isolating the capacitors upon adisparity in voltage whereby the generating device operates withoutregard to opening of the switch.

15. rl'he combination as set forth in claim 14 together with means forquickly recharging said control capacitor upon opening of said switch.

No references cited.

ARTHUR GAUSS, Primary Examiner. B. P. DAVIS, Assistant Examiner.

1. IN AN ELECTRICAL MUSICAL INSTRUMENT: AN ELECTRICALLY OPERATED GENERATING DEVICE THAT PRODUCES A SIGNAL CORRESPONDING TO A MUSICAL TONE WITH AN INTENSITY RELATED DIRECTLY TO THE INTENSITY OF ELECTRICAL ENERGIZATION: AN OPERATING CAPACITOR; AN OPERATING CIRCUIT FOR SAID GENERATING DEVICE INCLUDING SAID OPERATING CAPACITOR; A SINGLE POLE KEY SWITCH COOPERABLE WITH A SOURCE OF DIRECT CURRENT; A CONTROL CAPACITOR; CIRCUIT MEANS PROVIDING CHARGING AND DISCHARGING CIRCUITS FOR SAID CONTROL CAPACITOR, AND OPERABLE RESPECTIVELY IN ACCORDANCE WITH THE POSITION OF SAID KEY SWITCH; AND UNIDIRECTIONALLY CONDUCTIVE MEANS INTERCONNECTING THE OPERATING CIRCUIT AND SAID CONTROL CAPACITOR UPON OPERATION OF SAID KEY SWITCH; SAID CIRCUIT MEANS HAVING CHARACTERISTICS DETERMINING THE CONTINUED EFFECTIVENESS OF SAID UNIDIRECTIONALLY CONDUCTIVE MEANS FOLLOWING KEY SWITCH OPERATION. 